Storage and expulsion system for viscous fluids



Nov. 9, 1965 E. F. VERSAW ETAL 3,216,621 STORAGE AND EXPULSION SYSTEM FOR VISCOUS FLUIDS Filed June 13, 1963 2 Sheets-Sheet 1 BERNARD L. MESSINGER BY 1965 E. F. VERSAW ETAL 3,216,621

STORAGE AND EXPULSION SYSTEM FOR VISCOUS FLUIDS Filed June 13, 1963 2 Sheets-Sheet 2 N 0 IO v o 3 co as v f o /KD .D 2 U 0 N) L YT LO LL.

U 0 IO 8 4 n .s 0) 0 0 j 1 as [Q O O 4 INVENTORS. I EDWARD F. VERSAW m i BERNARD L.MESSINGER I m BY S H m Agent United States Patent 3,216,621 STORAGE AND EXPULSION SYSTEM FOR VESCGUS FLUHDS Edward F. Vet-saw, La Canada, and Bernard L. Messinger,

Sherman Gales, Califi, assignors to Lockheed Aircraft Corporation, Burbank, Calif.

Filed June 13, 1963, Ser. No. 287,715 14 Claims. (Cl. 22295) This invention relates to fluid storage and expulsion system and more particularly to storage and expulsion systems having optimum volumetric efliciency when utilized with irregular shaped container bodies and the capability of maintaining center of gravity control during positive expulsion sequences.

Fluid storage systems wherein there exists a requirement for the positive expulsion of the fluids contained therein have heretofore been deficient in several aspects. Particularly, with relation to fluids of high viscosity, it has generally been necessary that a piston and cylinder configuration be utilized for positive expulsion purposes. Due to irregularities in outer tank configurations, it has not heretofore been possible to efficiently utilize the total available storage capacity. Major problems have also been encountered as a result of gravity shifts caused by asymmetric expulsion of fuel from the storage container and resultant from the necessity of storing and discharging fluids too viscous to flow under normal gravity forces. The provision of insulating means whereby the transfer of heat from the skin of a rapidly moving vehicle into the fluid of the storage container has also provided considerable dilficulty in prior art vehicles.

Through utilization of the present invention considerable progress has been achieved in overcoming these prior art deficiencies. A major object of this invention is to provide a fluid storage and expulsion system wherein the maximum available storage space is utilized irrespective of tank shaped irregularities while retaining the capability of positively expelling substantially all fluid from the system.

Another object is to program propellant withdrawal from the system such that a maximum thermal barrier in the form of pressurizing gas is provided between the outer skin and the propellant responsive to radial movement of a flexible tank as early in the operational phase as practicable.

Another object of the invention is to provide propellant expulsion means wherein the center of gravity re mains substantially constant throughout the expulsive sequence.

Still another object of invention is to provide a tank and expulsion system wherein a flexible tank of irregular shape surrounds a longitudinally extending tank of regular cross-sectional configuration to provide means for positively expelling all propellants from tanks of irregular shapes responsive to controlled pressure actuation.

A further object is to provide a plurality of flexible tank segments surrounding a plurality of tubular members for cooperatively accomplishing fluid expulsion from an irregularly shaped container. These and other related objects of the invention will become apparent from the following description of certain preferred embodiments described herein and illustrated in the accompanying drawings in which:

FIGURE 1 is a semi-schematic elevational view of a preferred embodiment of the invention partially cut away to better illustrate the structural characteristics of the invention;

FIGURE 2 is a cross-sectional 22 of FIGURE 1;

FIGURE 3 is an enlarged cross-sectional view taken along line 33 of FIGURE 1;

view taken along line FIGURE 4 is an enlarged view of a typical outer peripheral piston seal; and

FIGURE 5 is a semi-schematic illustration of an alternate embodiment of the invention utilizing a plurality of tank segments.

The invention finds its principle application in the flyable vehicle art as related to the storage and expulsion of propellants. Therefore, while the invention is not to be considered as so limited, it is generally discussed herein with respect to propellants.

A basic configuration of the invention comprises an outer shell or tank of predetermined configuration, either regular or irregular in shape, a tubular member of constant cross-section and including a multiplicity of perforations being disposed longitudinally within the outer shell and a flexible tank member being sealably attached to the perforated tubular member, the flexible tank member adapted for expansion into intimate contact with the outer shell by tanked fluid. A pair of pistons positioned within the perforated tubular member at opposite extremities thereof are adapted to be pressure actuated to converge in a mutually uniform manner toward the center of the perforated member. Pressurization control means is provided to externally pressurize the flexible tank member preliminary to piston actuation such that propellant is forced from exit means responsive to sequential pressurization, the propellant contained between the flexible member and the perforated member being first forced into the interior of the perforated member and the remaining propellant being subsequently expelled responsive to piston actuation.

In greater detail, FIGURE 1 illustrates a preferred embodiment of the storage and expulsion system, the numeral 10 designating the over-all system. Since a typical application of the invention may be to an aircraft or a missile, the outer skin 12 may be the outer skin of a vehicle proper to which the system is applied. In such event, the skin provides an integral portion of the present system. The skin 12 is provided with a plurality of formers or stilfeners 14 structurally afiixed to its internal surface for structural support.

Positioned substantially concentrically within the other skin 12 is a longitudinally extending tubular member 16 including a multiplicity of performation 13. The tubular member 16 is structurally aflixed to the outer skin 12 through a pair of connector rings 20. A series of stitfener ring 22 are provided about the periphery of the tubular member 16 at predetermined longitudinal intervals for purposes of structural rigidity and for a further purpose to be hereinafter described. The tubular member 16 is provided with sealed bulkheads 24 and 26 at its opposite extremeties and is of constant cross-section, usually cylindrical, in each of its functional sections.

A flexible tank member 28, sometimes referred to as a bladder, is positioned between the tubular member 16 and the outer skin 12 and is substantially coextensive in length with the tubular member 16. This flexible tank member may be sealed in any convenient manner to the outer surface of the tubular member 16. The conventional sealing method used in the particular embodiment is dependent upon the material from which the flexible tank member is fabricated. For example, when the flexible tank member 28 is fabricated from the reaction product of terephthalic acid and ethylene glycol cast as a sheet and bilaterally stretcher (commercially known as Mylar), it may be adhesively bonded and/or clamped about the ends of the tubular member 16 in accordance with standard and conventional technique. When a flexible metallic material is utilized for the tank member 28, it may be welded, brazed or otherwise conventionally secured to the tubular member 16. The feature of significance with respect to the bond is that it must be of sufficient strength to withstand pressures exerted from both within and without the flexible tank member without leakage.

It is preferable that the corners of the formers 14 which extend interiorally of the outer skin 12 be rounded in order that they do not perforate the flexible tank member 28 when the flexible tank is forced thereagainst. The formers 14 should extend radially into the tank a minimum distance while still providing required structural integrity. A pressure distribution line 30 leads from a hereinafter described pressurization system and extends the length of the outer skin 12, passing through the formers 14 (see FIGURE 3). The distribution line 36 includes a plurality of pressurization gas outlets 32 in the regions of the formers 14 for uniformly pressurizing the flexible tank member 28 and forcing it inwardly against the outer circumference of the tubular members 16.

An insulating material 34 is usually disposed against the interior surface of outer skin 12 between formers 14 for minimizing the transfer of heat from the skin to the propellant.

A pair of pistons 36 and 38 are slideably positioned interiorly of the tubular member 16 at opposite tubular extremities. A piston guide 40 having a pressure transfer line 43 extended therethrough is positioned concentrically within the tubular member 16. The piston 36 includes a perforated boss 42 conventionally sealed, as by an O ring 44, and encircling the piston guide 40 for guiding the piston 36 in its longitudinal travel. As best illustrated in FIGURE 4 the piston 36 additionally contains an O ring seal 46 in its outer periphery. This seal, which is typical of seals so used in similar pistons of the invention, is forced to traverse the perforations 18 as the piston 36 travels along the length of the perforated tubular member 16. The O ring 46 is configured for deformation sufficient to provide sealing between the piston 36 and the tubular member 16 as the piston traversal is accomplished. It is preferably manufactured from a relatively hard material having lubricant properties. The commercial Mylar is an example of a suitable material for this use. The O ring 46 preferably includes thickened wall sections 48 and 50 at its outer and inner extremities, respectively, and thinned sections, such as illustrated at numeral 52, to provide flexibility for sealing ring deformation. The thickened portion 48 also provides resistance to abrasion as the O ring 48 traverses the perforations 18.

The piston guide 40, at its end opposite of the bulkhead 24, includes a plurality of fins 54 extending radially outward into contact with a second piston guide member 56. The guide member 56 is concentrically positioned with respect to the guide member 40 and the perforated tank member 16 by the bulkhead 26 and a web 58. The latter web includes a plurality of perforations 60 adapted to accommodate fluid transfer therethrough. The piston 38 is guided in its traversal of the tubular member 16 by the guide 56 by virtue of a sealed piston boss 62. The piston guide 56 also provides a fluid exit for the fluid normally contained within the system and to be expelled therefrom.

Pressure for propellant explusion is provided by a series of conduits interconnected with the pressure receiving surface through appropriate control and proportioning valves. The line 64 leads from a gas pressure source (not shown) through a pair of pressure regulators 66 and 68. The pressure distribution line 30 transfers regulated gas from the pressure regulator 66 through the bulkhead 20 and distributes it via the outlets 32 into the pressure receiving regions adjacent the formers 14. At these positions the flexible tank 28, in its traversal of the formers 14, defines a series of small annular openings with respect to the formers. An even distribution of pressure around the flexible tank 28 is thereby provided. It is sometimes desirable that annular branch lines (not shown) from the distribution line 30 be provided in the regions of the formers 14 in order that pressure may be controllably distributed evenly about the circumference of the tank. A plurality of distribution lines 30 are sometimes used. The pressure regulator 68 transfers pressurized gas, at a somewhat lower pressure than that passed by the pressure regulator 66, into a flow proportioner 7 tl. A line '72 directs a portion of the pressurization gas through the bulkhead 24 and into the pressure receiving region between the bulkhead 24 and the piston 36 to force the piston 36 toward the center of the tubular member 16. The line 42 from the flow proportioner 76 leads through the guide member 40, the guide member 56 and the bulkhead 26 to provide pressurization of the region between the bulkhead 26 and the piston 38, the pressure so provided being substantially proportional to the supplied between the bulkhead 24 and piston 36.

In filling the system with propellant the flexible tank 28 is positioned in contact with the outer extremity of the tubular member 16 and the pistons 36 and 38 are moved to a central position within the tubular member, abutted against the web 58. This may be accomplished through activation of the pressurization system. The propellant is then forced into the system under pressure in the direction of the arrow 74 through the guide member 56 and into the interior of the tubular member 16 such that the force of the fluid acts against the pistons 36 and 38 to separate them into the positions illustrated in FIGURE 1. As the pistons are so separated a portion of the propellant is transferred through the perforations 18 to the exterior of the tubular member 16, forcing the flexible tank 28 outward into the position of FIGURE 1. This action is con tinued until such time as the system is completely filled.

An operational procedure in expelling the tank fluid is accomplished in a manner substantially opposite to the filling procedure. Pressurized gas from a gas source is transferred through the line 64 and the regulator valves 66 and 68. In a representative system wherein the propellant outlet line (piston guide 56) was of a three and one half inch diameter, the pressure passed by the regulator 66 to the flexible tank member 28 by the distribution tube 30 was approximately 120 p.s.i. The pressure actuating the pistons 36 and 38, as controlled by regulator 68, was approximately p.s.i. Hence, during system operation under these or similar conditions, the tanked fluid is subjected to p.s.i. responsive to pressure transmitted to the flexible tank 28 via the distribution conduit 30 and outlet ports 32, the pressure being substantially equally distributed over the length of the flexible tank. The result of such controlled action is that substantially the entire flexible tank is forced inward simultaneously rather than its being subjected to a progressive pressurization action emanating from a single end of the tank. This equal pressure distribution prevents to a substantial degree any overlapping of tank segments and resultant trapping of fluid. As the pressurization continues, the flexible tank 28 is forced radially inward into intimate contact with the exterior of the tubular member 16, causing propellant interposed therebetween to be forced through the perforations 18 and into the interior of the tubular member 16. In turn, this action forces a portion of the propellant from the interior of member 16 into the conduit 56, to bypass the webs 54 and exit from the system in the direction of the arrow 76. As the flexible tank 28 contacts the outer surface of the tubular member 16 the support rings 22 take up a portion of the slack so as to prevent excessive buckling of the flexible tank.

When the flexible tank member 28 is forcibly engaged with the exterior of member 16, the fluid in the tank is no longer subjected to the higher actuation pressure (e.g. 120 p.s.i.) and the lower pressure (e.g. 100 p.s.i.) acting upon the pistons 36 and 38 causes those pistons to be forced toward one another, ultimately into abutting relation against the web 58, the fluid contained within the tubular member 16 being forced from the system as the pistons converge. Should either of the pistons 36 ch38 move more rapidly than the other, the pressure actuating the faster removing piston, resultant from the controlling action of the proportioning valve 70, is lowered and that piston then slows in its movement until such time as the pressure is equalized resultant from a like movement of the opposite piston. Hence, throughout system operation the fluid is expelled therefrom in a specifically controlled manner in substantially a proportional or balanced relation with respect to the center of gravity of the system. The center of gravity in the system and its tanked fluid is thereby maintained constant irrespective of the amount of fluid contained or the stage of the expulsion sequence.

Under certain circumstances it is sometimes desirable that alternate configurations of the invention be provided. This is particularly true in circumstances wherein the change in diameter of the outer container is sufliciently great over the length of the tanking system to prevent accurate control of the flexible tank and/or to result in an undue amount of folding or buckling of such tank. FIGURE 5 of the drawings semi-schematically illustrates a typical system a wherein tubular portions of lesser external diameter than a central tubular member are provided at each end thereof. This figure is illustrated only in suflicient detail to provide an understanding of portions of the system which differ substantially from the system of FIGURE 1, the central portion thereof being substantially the same in structure and function as heretoiore explained. In FIGURE 5 it will be noted that basic sections A, B and C are provided and that section A is basically similar to the system of FIGURE 1. The guide member 56a, rather than terminating at a position centrally of the perforated tubular member 16, extends through the entire length thereof and terminates in a bulkhead 78. Hence, the guide member and expulsion tube 56a replaces the guide member 4-6 of FIGURE 1 in section A and the boss 42a of the piston 36a has an enlarged central bore to accommodate the enlarged diameter. The guide 56:: also includes a series of perforations or slots 80 through which the fluid from the tubular member 16 may exit.

A pair of secondary perforated tubular members 16a and 165 are respectively sealed by pairs of bulkheads 78 and 73a and S2 and 82a, and are surrounded by a pair of flexible tank members 28:: and 28b secured in a manner similar to that described with respect to the flexible member 28. The flexible members 280 and 281') are of lengths such that when secured and positioned in the manner illustrated in FIGURE 5 their pressurization results in their being flexed inwardly against the tubular members 16a and 1617, respectively, without substantial stretching of the flexible materials. The distribution line 30a leading into the region externally of the flexible tank 23a may be terminated therein, or alternatively, it may be utilized as a common supply line for each of the discrete regions of the system of FIGURE 5. in the first alternative form it is necessary that separate sections of the distribution line 39a be provided leading to each of the flexible tank sections. It is also sometimes desirable that the end tank portions be pressurized at a higher pressure than is the central portion in order that the external portions of the sections are emptied preliminary to actuation of the central portion. In such case, a separate pressure regulator valve and proportioning valve is provided to control the higher pressures required for sequencing. However, in the preferred embodiment of FIGURE 5 the sections A, B and C are pressurized simultaneously in order that the flexible tanks in all three sections are simultaneously emptied. A pair of pistons 84 and 86 disposed at opposite ends of the perforated tubular members 16a and 1612, respectively, are pressurized by means of pressure lines 88 and 90 for coordinated movement toward and ultimately into abutment with bulkheads 7S and 82, respectively, subsequent to the completion of actuation of the flexible tank members 280 and 28b.

The configuration of FIGURE 5 is sequenced through the control of appropriate valves of substantially the nature heretofore described with respect to FIGURE 1 such that the flexible tanks are first pressurized with a predetermined pressure until all fluid contained between the respective flexible tank members and their associated perforated tubular members is expelled. A second and lower pressure is then applied to the pistons 84 and 86 until such time as the balance of the fluid contained within the tubular members 16a and 16b is expelled through the conduit 56a. A third and lowest pressure is next applied to the pistons 36a and 38a to complete the fluid expulsion in the manner heretofore described. Tank bulkheads may be varied in accordance with good design principle. It is sometimes desirable that a single bulkhead such as indicated by numeral 92 be provided to separate the tank section, rather than utilizing a plurality of bulkheads such as shown at the opposite tank extremity.

Through the novel combination of elements described herein it has become possible to positively expel fluids, particularly those of high viscosity, from an irregularly shaped tank while utilizing the maximum available storage volume and without substantial change in the center of gravity of the vehicle to which the invention is adapted. Radial displacement of the flexible tank, since it is sequentially the first to be so moved responsive to applied pressure, also results in thermal isolation of tanked propellant from the outer skin of the tank.

While specific embodiments of the invention have been shown and described in sufficient detail to enable the invention to be practiced, it is to be understood that certain alterations, modifications and substitutions may be made to the instant disclosure without departing from the spirit and scope of the invention as defined by the appended claims.

We claim:

1. An expulsion system for fluid comprising:

(a) longitudinally extending rigid tank means;

'( b) flexible tank means disposed within said rigid tank means and adapted to be deformed inward responsive to the application of pressure between said rigid tank means and said flexible tank means;

(c) radially perforated cylinder means substantially coextensive with said flexible tank means and secured thereto for containing fluid and for accepting fluid forced from between said flexible tank and said cylinder means;

(d) piston means in said cylinder means adapted to force fluid from said cylinder means centrally thereof and in substantially equal amounts ends of said cylinder; and

(e) pressurization means for sequentially pressurizing the exterior of said flexible tank and said piston means.

ameters, said flexible tank means is a plurality of flexible members substantially co-extensive with respective ones of said cylinders, and said piston means is at least one piston in each said cylinder.

3. A fluid storage and expulsion system comprising: (a) rigid tank means; (b) flexible tank means within said rigid tank means, said flexible tank means substantially conforming to of said rigid tank means;

'(c) a perforated tubular member having closed ends sealably connected to said flexible tank means to define a complete scaled tank therewith for fluid storage;

(d) dual piston means positioned within said tubular member at opposite extremities thereof;

(c) fluid conduit means leading from a position substantially centrally of said tubular means to the exterior of said system for transmitting fluid being expelled from said system; and

(f) pressurization and control means leading to the exterior of said flexible tank means and to regions between said ends of said tubular member and said piston means so as to sequentially force said flexible tank means against said tubular member and move said piston means to a position centrally of said tubular member, thereby expelling substantially all stored fluid from said system.

4. The fluid storage and expulsion system of claim 3 further comprising:

(a) a pressure distribution line extending over the length of said flexible tank means between said flexible tank means and said rigid tank means, said line being provided with outlets at discrete locations along the length thereof to provide a substantially equal pressure distribution along the entire length of said flexible tank.

5. The fluid storage and expulsion system of claim 3 further comprising:

(a) a pressure distribution line extending over the length of said flexible tank means between said flexible tank means and said rigid tank means, said line being provided with outlets at discrete locations along the length thereof to provide a substantially equal pressure distribution along the entire length of said flexible tank;

(b) ring means circumferentially secured to the interior of said rigid tank means for structural support there -of and for providing a plurality of longitudinally spaced annular pressure distribution regions for equalizing pressurization of said flexible tank; and

(c) a plurality of ring members exteriorly spaced along the length of said tubular member and extending radially outward therefrom to stiffen said tubular member and to prevent excessive folding of said flexible tank during fluid expulsion.

6. The fluid storage and expulsion system of claim 3 wherein said pressurization and control means includes pressure regulators respectively regulating pressurizing gas directed between said rigid tank means and said flexible tank means to a predetermined pressure and regulating gas directed to said slidable piston means to a predetermined lower pressure whereby fluid is expelled from a region defined between said flexible tank and said tubular member before said piston means.

7. A fluid storage and expulsion system comprising:

(a) rigid tank means for receiving a fluid;

(b) a peripherally perforated cylindrical member fixed interiorly of said tank means with respect thereto and having bulkheads sealably closing ends thereof;

(c) flexible tank means surrounding said cylindrical member interiorly of said rigid tank means and sealed to the ends of said cylindrical member for containing fluid between said flexible tank means and said cylindrical member and interiorly of said cylindrical member;

(d) a pair of pistons slidably positioned within said cylindrical member at opposite ends thereof for movement toward one another;

(e) fluid exit means leading from a central region of said cylindrical member; and

(f) pressurizing means for expelling the contained fluid by sequentially forcing said flexible tank into contact with said cylindrical member and causing said pistons to move to the center of said cylindrical member in a substantially uniform manner.

8. The fluid storage and expulsion system of claim 7 further comprising:

(a) piston guide means concentrically positioned within said cylindrical member and through said pistons, said piston guide means including a portion having means for accepting and transmitting fluid being expelled from said system, an inlet to said portion being positioned substantially centrally of said cylindrical member.

9. The fluid storage and expulsion system of claim '7 wherein said rigid tank means includes structural formers extending radially inward therefrom and an insulation material is disposed against said rigid tank means between said formers.

10. A storage and expulsion system for fluids compris- (a) a cylindrical tube including a wall having a multiplicity of perforations therethrough and having bulkheads closing its ends;

(b) a perforated web extending radially inward from said wall centrally of said cylindrical tube;

(0) a fluid conduit positioned concentrically within said cylindrical tube and having one end connected to said web and the other end extending through one of said bulkheads, said one end providing a fluid outlet from said cylindrical tube;

(d) a piston guide positioned concentrically within said cylindrical tube between said web and the other of said bulkheads;

(e) a pair of pistons slidably and sealably positioned within said cylindrical tube adjacent said bulkheads and movable into abutment with said web, said pistons being respectively guided in their movement by said fluid conduit and said piston guide;

(f) a flexible tank circumferentially encompassing said wall of aid cylindrical tube and sealed to ends thereof adjacent said bulkheads, said flexible tank being pressure actuatable into intimate contact with said tube;

(g) a rigid tank circumferentially encompassing said flexible tank and adapted to be contacted by said flexible tank in a supporting relation when said flexible tank is filled with fluid; and

(h) pressurization means positioned and controlled to sequentially force said flexible tank into contact with said cylindrical tube and to move said pistons into abutment with said web, thereby expelling fluid from said system without substantial change in the center of gravity thereof.

11. The storage and expulsion system of claim 10 wherein a pair of pressure regulators are provided in said pressurization means to direct pressurizing ga to said flexible tank at a predetermined higher pressure than to said pistons.

12. The storage and expulsion system of claim 10 wherein said pistons are provided with seals in their outer peripheries, said seals being of sufficient width and material thickness to facilitate traversal of said perforations without substantial loss of system-contained fluid or injury to said seal.

13. The storage and expulsion system of claim 19 wherein said pistons are provided with hollow annular seals in their outer peripheries, said seals being of substantially thinner cross-section at lateral sides thereof than at their radially displaced sides, said radially displaced side positioned to slidably contact said cylindrical tube of being a thickness and stiffness sufficient to prevent its entrapment by said perforations.

14. A system for containing and positively expelling fluids of high viscosity comprising:

(a) a rigid tank;

(b) a first flexible tank centrally disposed within said rigid tank;

(c) second and third flexible tanks of smaller diameter than said first tank disposed within said rigid tank outward from said first tank upon a common longitudinal axis therewith and at opposite ends thereof;

(d) a first radially perforated cylindrical member coextensive with and sealed internally of said first flexible tank;

(e) second and third radially perforated cylindrical members respectively co-extensive with and sealed 9 to said second and third flexible tanks and afiixed to said first cylindrical member upon a common axis therewith;

(f) a piston slidably positioned at each end of said first cylindrical member interiorly thereof for pressure actuated movement to a central position;

(g) a piston slid-ably positioned in an outer end of each of said second and third cylindrical members for pressure actuated movement to the opposite ends thereof toward said first cylindrical member; and

(h) pressurization and control means for sequentially forcing said flexible tanks into intimate contact with their respective cylindrical members, simultaneously moving said pistons within said second and third cylindrical members to said opposite ends, and simultaneously moving said pistons in said first cy- Iindrical member to the center thereof, thereby positively expelling any fluid contained in said system without substantially changing the center of gravity of said system.

No references cited.

EVERETT W. KIRBY, Primary Examiner. 

1. AN EXPULSION SYSTEM FOR FLUID COMPRISING: (A) LONGITUDINALLY EXTENDING RIGID TANK MEANS; (B) FLEXIBLE TANK MEANS DISPOSED WITHIN SAID RIGID TANK MEANS AND ADAPTED TO BE DEFORMED INWARD RESPONSIVE TO THE APPLICATION OF PRESSURE BETWEEN SAID RIGID TANK MEANS AND SAID FLEXIBLE TANK MEANS; (C) RADIALLY PERFORATED CYLINDER MEANS SUBSTANTIALLY COEXTENSIVE WITH SAID FLEXIBLE TANK MEANS AND SECURED THERETO FOR CONTAINING FLUID AND FOR ACCEPTING FLUID FORCED FROM BETWEEN SAID FLEXIBLE TANK AND SAID CYLINDER MEANS; (D) PISTON MEANS IN SAID CYLINDER MEANS ADAPTED TO FORCE FLUID FROM SAID CYLINDER MEANS CENTRALLY THEREOF AND IN SUBSTANTIALLY EQUAL AMOUNTS FROM OPPOSITE ENDS OF SAID CYLINDER; AND (E) PRESSURIZATION MEANS FOR SEQUENTIALLY PRESSURIZING THE EXTERIOR OF SAID FLEXIBLE TANK AND SAID PISTON MEANS. 